1. Field of the Invention
The present invention relates to an electric suspension device and a motorcycle including the electric suspension device.
2. Description of the Related Art
A conventional rear suspension device for a motorcycle includes a monotube-type cylinder and a twin tube-type cylinder. Depending on the type of rear suspension, a tank separate from the cylinder may be provided such as a sub-tank or a bladder tank.
A suspension device described in Japanese Unexamined Patent Publication No. H02-14992 includes a rear suspension including a monotube cylinder and a bladder tank connected to the interior of the cylinder. The interior of the bladder tank is connected to the interior of the cylinder via a dedicated oil passage.
A twin-tube cylinder includes an inner tube that houses a piston and an outer tube that surrounds the inner tube. The interior of the inner tube is partitioned into two inner oil chambers (first inner oil chamber and second inner oil chamber) by the piston. The first inner oil chamber is connected to a tubular space (outer oil chamber) between the inner tube and the outer tube via a first oil passage, and is also connected to a tank separate from the cylinder such as a bladder tank via a second oil passage.
Twin-tube cylinders are better than monotube cylinders in that the stroke is long and the oil pressure is lowered. These advantages contribute to an improvement in the riding comfort of a vehicle driver/passenger, and have a great effect particularly on a touring type vehicle. However, as described above, a twin-tube cylinder not only includes a plurality of tubes but also includes a plurality of oil passages connected to the oil chambers, and is therefore structurally likely to have a larger outer diameter than that of a monotube cylinder. In other words, when the monotube cylinder is simply replaced with a twin-tube cylinder in the suspension device of Japanese Unexamined Patent Publication No. H02-14992, the suspension device is increased in size. Particularly, if the plurality of oil passages connected to the respective oil chambers are not appropriately arranged, the suspension device is further increased in size. Moreover, if the plurality of oil passages are respectively independent, not only are many components corresponding to the respective oil passages required, but the processing man-hours also increase.
Moreover, the suspension device of Japanese Unexamined Patent Publication No. H02-14992 includes a damping force adjusting mechanism disposed at an over-spring portion (portion above the spring). However, the suspension device including a monotube cylinder and a damping force adjusting mechanism disposed at an over-spring portion is more likely to suffer a degradation in damping performance caused by cavitation than in a suspension device including a monotube cylinder and a damping force adjusting mechanism disposed at an under-spring portion (portion below the spring). On the other hand, when a suspension device includes a damping force adjusting mechanism that adjusts a damping force by electrical equipment such as an electric motor disposed at an under-spring portion, because vibrations and shocks accompanying traveling are transmitted to the electrical equipment before being relieved by the spring, the electrical equipment vibrates more severely than when the electrical equipment is disposed at an over-spring portion, so that the electrical equipment may have a reduced durability. Therefore, designs with vibrations of electrical equipment and the like taken into consideration is required.